1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive for storing sector-reconstruction sectors and for storing a sector-reconstruction status in sectors distributed around a disk.
2. Description of the Prior Art
A disk drive comprises a disk for storing data in radially spaced, concentric tracks. Each track is partitioned into a plurality of data sectors, and user data is written to the disk a sector at a time. A special timing pattern referred to as a preamble as well as a sync mark are recorded at the beginning of each data sector to facilitate synchronizing to the data during read back. A sector level error correction code (ECC), such as a Reed-Solomon code, is also typically employed to detect and correct errors in the data induced by imperfections in the recording and reproduction process. With the sector level ECC, special redundancy symbols are generated over the user data during a write operation and then recorded with the user data in a data sector. During read back, the redundancy symbols are used to detect and correct errors in the user data. However, if the number of errors exceeds the correction power of the sector level ECC, or if the preamble or sync mark in the data sector is unreadable, the data sector becomes unrecoverable at the sector level.
U.S. Pat. No. 5,872,800 discloses track level parity for reconstructing a data sector unrecoverable at the sector level. With the track level parity, each track comprises a parity sector for storing track level parity generated over the data sectors in the track. A data sector unrecoverable at the sector level can be reconstructed at the track level by computing the parity over the other data sectors together with the parity sector.
FIG. 1A shows a prior art disk drive comprising a disk 4, a head 6, and an actuator 8 for actuating the head 6 radially over the disk 4. The disk 4 comprises a plurality of radially spaced, concentric data tracks each comprising a plurality of data sectors (e.g., D0-D14) and a track level parity (TP) sector. The disk 4 is partitioned into a plurality of zones (e.g., inner zone 10 and outer zone 12) wherein the data rate is increased from the inner to outer zones in order to achieve a more constant linear bit density. As shown in FIG. 1B, each data sector comprises a preamble field 14 and a sync mark field 16 for use in synchronizing to user data stored in a data field 18. ECC redundancy symbols 20 are appended to the end of the data sector and used to detect and correct errors in the user data during read back. The TP sector stores parity data generated over the data stored in the data sectors (e.g., D0-D14). The TP sector also stores a TP status bit S 22 which indicates the validity of the TP sector.
The ""800 patent also discloses to cache write parity (WP) sectors to improve performance by avoiding the rotational latency associated with updating the TP sector of a track. Multiple writes to the same track will update the cached WP sector rather than rewriting the TP sector to the disk. The cached TP sectors are regenerated and written to the disk during idle time, thereby avoiding the rotational latency of writing the TP sectors during normal write operations. When a WP sector is cached, a TP status (bit S 22 of FIG. 1A) is updated in the TP sector stored on the disk to indicate that the disk TP sector is no longer valid. This prevents the use of the disk TP sector in the event the cached WP sector is lost due to a power failure. However, there is an undesirable rotational latency associated with storing the TP status in the disk TP sector at the end of a normal write operation. The disk drive must wait for the disk to rotate until the head reaches the TP sector in order to write the TP status to the disk TP sector.
There is, therefore, a need to reduce the rotational latency associated with storing a status of a sector used to reconstruct other sectors in a disk drive.
The present invention may be regarded as a disk drive comprising a disk, a head, and an actuator for actuating the head radially over the disk. The disk comprises a plurality of tracks, wherein each track comprises a plurality of sectors. The plurality of sectors comprise a plurality of data sectors for storing data and at least one sector-reconstruction (SR) sector for storing redundancy data generated in response to the data stored in at least one of the data sectors. At least two of the plurality of sectors of a track are for storing a SR status indicating a validity of the SR sector stored on the track.
In one embodiment, the at least one SR sector comprises a plurality of sector-reconstruction-interleave (SRI) sectors for storing redundancy data. The redundancy data stored in each SRI sector is generated in response to the data stored in an interleave of the data sectors, and the plurality of SRI sectors for storing the SR status. In one embodiment, the redundancy data stored in at least one of the SRI sectors is generated by computing a parity over the data stored in an interleave of the data sectors. In an alternative embodiment, the data stored in each interleave of the data sectors represent data polynomials, and the redundancy data stored in the SRI sectors is generated by dividing the data polynomials by a generator polynomial. In one embodiment, when the disk drive receives write data from a host to be written to a track on the disk, the disk drive generates a write-reconstruction (WR) sector over the write data and stores the WR sector in the semiconductor memory. The disk drive writes the write data to at least one of the plurality of data sectors, and the disk drive writes the SR status to at least one of the at least two sectors for storing the SR status.
The present invention may also be regarded as a disk drive comprising a disk comprising a plurality of tracks, each track comprising a plurality of sectors, the plurality of sectors comprise a plurality of data sectors for storing data and at least one sector-reconstruction (SR) sector for storing redundancy data generated in response to the data stored in at least one of the data sectors. The disk drive further comprises a head, an actuator for actuating the head radially over the disk, and a disk controller. The disk controller for writing data to the data sectors, writing the redundancy data to the SR sector, and writing an SR status to at least two of the plurality of sectors, the SR status indicating a validity of the SR sector.
The present invention may also be regarded as a disk controller for use in a disk drive. The disk drive comprising a disk comprising a plurality of tracks, each track for storing a plurality of sectors, the plurality of sectors comprise a plurality of data sectors for storing data and at least one sector-reconstruction (SR) sector for storing redundancy data generated in response to the data stored in at least one of the data sectors, a head, and an actuator for actuating the head radially over the disk. The disk controller comprising a means for writing data to the data sectors, a means for writing the redundancy data to the SR sector, and a means for writing an SR status to at least two of the plurality of sectors, the SR status indicating a validity of the SR sector.